[Evolution] export message to mbox and then process with script

["Gilchrist, Michael Aaron" <mikeg utk edu>]

I often want to save a message as a simple txt file.
Currently, I export a message I want to save to a .mbox file and then run a
script on it to extract the text.  The script uses the From, Date, and Subject
information to automatically generate a meaningful file name.  I'm wondering how
I can automate this.

I see on the webbernet to using pipes and, alternatively, filters, but can't seem
to find the relevant documentation.

Any help will be appreciated.
Mike